This invention relates to the production of a substantially rigid plastic socket for receiving the stump or residual limb of a partial amputee, such as, for example, a prosthetic limb socket as disclosed in U.S. Pat. No. 5,980,803 and U.S. Pat. No. 6,551,683, the disclosures of which are herein incorporated by reference. In the forming of a socket in accordance with U.S. Pat. No. 5,980,803, it is common to extrude a large rectangular flat sheet of thermoplastics material and with a predetermined thickness, such as one-half inch, and then cut the sheet into a plurality of smaller square pieces or sheets, for example, 24 inch square sheets. A peripheral portion of a square sheet is clamped within a square metal clamping frame and the square frame and sheet are placed within an oven having a temperature of about 400° F. and until the square plastic sheet softens. The heated square plastic sheet and the attached square frame are then removed from the oven by manually gripping the frame with protective gloves, and the sheet is drawn and stretched downwardly over a hollow positive model of the stump or residual limb.
In accordance with U.S. Pat. No. 6,551,683, which issued to an inventor of the present invention, a metal reinforcing ring is molded within a peripheral portion of an injection molded disk. The positive model is commonly mounted on a vacuum base or pedestal which creates a vacuum within the hollow model and through fine holes or pores within the model while the heated plastic sheet or disk is stretched over the model to form a socket conforming to the model. The positive model of the patient's residual limb is commonly produced by forming a plaster cast on the patient's residual limb, removing the cast after it hardens and filling the cast with a plaster to make a positive model. The cast is then removed or broken away from the positive model with a pneumatic chisel. A positive model may also be made, for example, as disclosed in U.S. Pat. No. 5,901,060, that is, by using a digitized impression of the residual limb to machine the model. After a socket is formed, it usually receives a coupler such as the socket coupler disclosed in U.S. Pat. No. 6,106,559 which issued to an applicant of the present invention.
It has been determined that the above method for making a socket using a square plastic sheet cut from a larger extruded sheet is slow and expensive and results in producing significant scrap from the sheet, primarily due to the square corner portions of the sheet which are scrapped along with the trimmed base portion of the drawn sheet used to form the socket. Also, the clamping frame for the rectangular sheet is relatively expensive, has a limited service life, and requires significant time to be properly attached to the peripheral portion of the square sheet and then removed from the sheet after the heated sheet is stretched over the positive model. The method of making the square sheet, the corner portions of the square sheet and the significant time required for attaching the clamping frame to the square sheet and removing the frame after forming a socket, add significantly to the cost of producing the socket. While the above method of making a socket with an injection molded disk having an embedded metal reinforcing ring significantly decreases the time required for making a socket, the reinforcing ring adds to the cost of the disk, and the ring is not reusable and becomes scrap along with the base portion of sheet or disk removed from the socket.